#but1,#but2{float:right;}
#but1{margin:0 50px 0 0;}
#reg,#login{
    border:1px solid red;
    width: 500px;
    height: 300px;
    margin:80px 0 0 250px ;
    position: absolute;
}
#reg{height: 400px;
    background-color: red;}
#login{
    background-color: lightgreen;
}

.yin{display: none;}
.xian{display: block;}



